Fukushima Two Years Later (part 1)

We have been hearing a lot about
the nuclear accident at the Fukushima Daiichi Nuclear Station in Japan this
week. There continues to be a great deal
of misunderstanding about the accident and nuclear issues in general so I
thought this would be a good time to spend some words. This is the first of six blogs about the
accident and the current state of commercial nuclear technology.

First of all, my background – (and
if I were in a group of nuclear techies, someone would surely say – "oh, I'd
say about 100 counts per minute"....... Ba-dum-BUM...it's a joke folks, just a bad
joke).

I am an environmental
radiochemist and retired State of Oregon nuclear regulator. I proudly serve on Oregon State University's
Nuclear Engineering and Radiation Health Physics (NERHP) Advisory Board. I am old enough to have measured fresh
fission product fallout from China in the 70's and to have measured environmental
concentrations of radioactive materials before the Trojan Nuclear Plant went
on-line and during the time a few of Hanford's Plutonium production reactors
were still operating. My last official
act as a state executive was to recommend approval of Trojan's final
decommissioning to the Oregon Energy Facility Siting Council in 2005. I currently spend my professional time as a
Middle and High school science teacher and occasionally as a nuclear safety
consultant.

What is now known as the Great East Japan Earthquake
began at 2:46 pm local time, March 11, 2011.
It was a magnitude 9 quake, and large by any measure. It's important to understand that earthquakes
are measured on a logarithmic scale where each whole number increment is 30
times the energy release of the previous number. If you hear anyone talk about the Richter
Scale for a large quake, you can be sure they don't know what they are talking
about. The Richter Scale is based on the
largest swing of a seismograph needle during an event. The problem is, larger earthquakes shake both
harder and longer and need a scale that measures the total energy released, not
just the magnitude of shaking. Current
measures of large quakes use the Moment Magnitude Scale. The quake resulted in a maximum acceleration
over half that of gravity, but sideways.
None of the reactors were designed to withstand this force, but safety
systems nonetheless operated as designed at first.

As big as it was, the major damage was caused by
the resulting tsunami arriving less than an hour later. Except for the tsunami,
there would likely not have been any release of radioactive material to the
environment at Fukushima. Sea water
flooded the rooms containing the emergency diesel generators, pumps and
electrical switching equipment. The
generators are designed to provide power to reactor circulation pumps in the
event of a loss of offsite power. These
pumps came on as designed, but were in a basement room and when water breached
the sea wall they were inundated. In
addition, newer back-up generators placed on a nearby hilltop as a precaution
against water damage were of no use because the switching gear needed to power
the pumps was by then under water.

Without a power source to keep the reactor cores
cool, they overheated and began to melt soon after. This heat is a result of the nuclear decay of
fission products in the reactor fuel, and requires the reactor core to be
actively cooled for weeks after shutdown.
To add to the problem, the zirconium alloy tubing holding the nuclear fuel
pellets begins chemically reacting with water when it gets above 1200 Cº. At a temperature of 1,852 Cº,
zirconium begins to melt and the zirconium/water reaction really speeds
up. The result of this reaction is the
production of zirconium oxide and hydrogen gas.

To protect the physical structure of the plant,
the Tokyo Electric Power Company (TEPCO) vented the reactor vessel into the
surrounding "dry well" to reduce internal pressure. However, the venting system of the reactor
building failed and an explosive mixture accumulated in the building and eventually
resulted in a hydrogen detonation. As a
result, the building was severely damaged and volatile radioactive isotopes
were released to the surrounding environment.